After a cagey opening ten minutes England put the first points on the board through Sharp who made no mistake with a well taken penalty, and he added his second with 23 minutes played to make it 6-0.
In what was a largely uneventful first period, Sharp saw a third kick sail wide before the first try eventually came through flanker Andrew Hughes, touching down after a rolling maul from a line-out to make the half time score 13-0.
England started the second half well and had their second try after 38 minutes (each half is 35 minutes) when Packman picked up the ball deep in his own half before beating three defenders and touching down under the posts, Sharp converted to make it 20-0.
England's third try came courtesy of another rolling maul, this time from over 22 yards out, and was eventually touched down by captain Chisholm - his third try in two games.
At 25-0 down Scotland began to play, and two late tries brought the score to 25-12, but England held out for the win, although Fletcher accepts that improvements will be needed ahead of Saturday's final.
He said: "I thought that overall we were quite poor to be honest, we didn't play to the standard that we expect and we'll have improve on that ahead of the final on Saturday. Massive credit to Scotland - they were physical, passionate and they played with real intent."
Points: Hughes 1T, Packman 1T, Chisholm 1T; Sharp 2P, 2C
England U18 starting XV to play Scotland
15. Howard Packman (Northampton Saints & Moulton College)
14. Tom Howe (London Wasps & Shiplake College)
13. Nick Tompkins (Saracens & Oaklands College)
12. Rory Jennings (Bath Rugby & Bryanston School)
11. Tom Fowlie (London Irish & St Paul's Catholic College)
10. Josh Sharp (Saracens & Oaklands College)
9. Stuart Townsend (Exeter Chiefs & Ivybridge College)
1. Luke Chapman (Exeter Chiefs & Truro College)
2. Jack Walker (Leeds Carnegie & Prince Henry's Grammar)
3. Paul Hill (Leeds Carnegie & Prince Henry's Grammar)
4. Jordan Onojaife (Northampton Saints & Stowe School)
5. Charlie Ewels (Bath Rugby & Bryanston School)
6. Andrew Hughes (Sale Sharks & Hartpury College)
7. Andrew Boyce (Worcester Warriors & Kings Worcester)
8. James Chisholm (Harlequins & Brighton College) (c)
16. Sam James (Saracens & Bishops Stortford) on for Jack Walker 65 mins
17. Lewis Boyce (Leeds Carnegie & Prince Henry's Grammar) on for Luke Chapman 47 mins
18. Neale Farthing (Leicester Tigers & Wyggeston & Queen Elizabeth College) on for Paul Hill 65 mins
19. Josh Peters (Northampton Saints & Oundle School) on for Jordan Onojaife 47 mins
20. Matt Bolwell (Exeter Chiefs & Truro College) on for Andrew Hughes 35 mins
21. James Mitchell (Sale Sharks & Lymm School) on for Stuart Townsend 57 mins
22. Josh Skelcey (Northampton Saints & Moulton College) on for Rory Jennings 65 mins
23. Louis Clayton-Molloy (London Wasps & Harrow School) on for Tom Howe 68 mins